1. Field of the Invention
This invention relates to a device for detecting pressure in a torque control wrench which is simple in construction and yet carries out precise detecting.
2. Description of the Prior Art
A shutoff mechanism, by which, when a set pressure is reached air supply to a motor is suspended to stop a wrench, is generally adopted for the torque control wrenches. According to this shutoff mechanism, a small hole communicating with a high pressure chamber of a liner is at an upper lid of the liner. A piston is moved inside the upper lid of the liner by the rise in pressure in the liner chamber upon the generation of pulse. A self-holding type detecting valve works in linkage with the piston. A timer circuit works in response to the detecting valve and a main valve is shut after the lapse of a certain preset period of time so as to stop working of a wrench.
However, when the above piston is moved by the rise of pressure, a spring pressure for returning the piston is always acting on the piston. The internal pressure at the time of the pulse is high and it is difficult to work out a spring design to cope with such an internal pressure. Theoretically, it is possible to change the timing of oil pressure detection by regulation of a spring but substantially, regulation of the timing is impossible. Since a timer operates after a preset pressure is reached, the tightening torque varies with variation of the state of the tightening work, and accordingly the tightening torque becomes unbalanced. Moreover, it becomes necessary to regulate the tightening time by means of output regulation by a relief valve shaft and a timer.
The present invention has for its object to dispense with the timer control, to equalize tightening torque and to carry out pressure detection precisely.